1. Field of the Invention
The invention relates to a trailing arm suspension for a vehicle; and, more particularly, to a height control valve for controlling the ride height of the suspension relative to the vehicle.
2. Description of the Related Art
Trailing arm suspensions are well known and are commonly used in heavy-duty vehicles, such as semi-tractor/trailer configurations. The trailing arm suspension comprises opposing trailing arm assemblies mounted on opposite sides of the vehicle, preferably the vehicle frame rails. Each of the trailing arm assemblies includes a trailing arm having one end pivotally connected to a hanger bracket suspended from the frame rail. The other end of the trailing arm mounts to an air spring, which is affixed to the frame rail. The air spring dampens the pivotal rotation of the trailing arm about the hanger bracket relative to the frame rail.
An axle assembly typically spans and mounts to, or is carried by, the trailing arms. The axle assembly rotatably mounts ground-engaging wheels. Any movement of the wheels in response to their contact with the ground will result in a rotation of the trailing arms, which is dampened by the air springs.
The air springs typically comprise an air bag from which pressurized fluid can be introduced or exhausted to adjust the dampening performance of the air spring. Additionally, the volume of air in the air spring can be adjusted to alter the height of the frame rails relative to the trailing arms. Often, there is a preferred ride height for the trailer and, depending on the load carried by the trailer, the ride height can vary. Pressurized air is introduced to or exhausted from the air bags to adjust the relative height of the trailer frame rail with respect to the trailing arms for a particular load.
The adjustment of the ride height is traditionally accomplished by a height control valve having an inlet port, an air spring port, and an exhaust port. The inlet port is fluidly connected to the pressurized air system of the vehicle. The air spring port is fluidly connected to the air bags of the air springs and, the exhaust port is fluidly connected to the atmosphere. The air spring port can be fluidly connected to either the inlet port or the exhaust port to introduce or exhaust pressurized air from the air springs. A three-position valve is typically used to provide for the fluid connections necessary to introduce and exhaust pressurized air from the air bags. The housing is typically mounted to the vehicle or vehicle frame and the lever arm is typically mounted to the trailing arm, whereby any movement of the lever relative to the valve housing is indicative of the relative change in position between the trailing arm and the vehicle.
The various height control valves currently available can be operated on a time delay or can respond instantly to changes in height. The valve structure for these valves typically includes multiple spring biased pistons or similar elements that seal the various ports in response to the relative movement of the trailing arm. Examples of this type of height control valve are disclosed in U.S. Pat. No. 5,161,579, issued Nov. 10, 1992; U.S. Pat. No. 5,560,591, issued Oct. 1, 1996; and U.S. Pat. No. 5,375,819, issued Dec. 27, 1994. These valves tend to use a seal in the form of an O-ring or the like that surround the dynamic or moving piston to seal the piston relative to the valve housing. These “dynamic” seals are subject to wear as the piston reciprocates, leading to their eventual failure.
Outside the context of a height control valve and in the context of a seat adjustment valve, it is known to use a shear valve structure to fluidly connect a pressurized air inlet port to an air cylinder or connect the air cylinder to atmosphere to extend or retract the air cylinder to raise and lower a vehicle seat. The shear valve comprises a chamber that is fluidly connected to the cylinder. A shear valve selectively connects the chamber to either an inlet port or an exhaust port to extend or retract the cylinder. The shear valve comprises a fixed disk positioned within the chamber with an opening connected to the cylinder and openings fluidly connected to the inlet port and the exhaust port. A rotatable disk having a passage that selectively overlies the inlet port opening and the exhaust opening is selectively rotated by the vehicle user to fluidly selectively connect the cylinder port to the inlet port or the exhaust port to extend or retract the cylinder to raise and lower the seat.
There is still a need for a height control valve that does not use traditional seals on dynamic elements of the valve while still providing consistently repeatable performance.